Biomass is of particular interest as a raw material due to its potential for supplementing and possibly replacing petroleum as a feedstock for the preparation of commercial chemicals. In recent years various technologies for exploiting biomass have been investigated. Carbohydrates represent a large fraction of biomass, and various strategies for their efficient use as a feedstock for the preparation of commercial chemicals are being established. These strategies include various fermentation-based processes, pyrolysis, and different processes, such as hydrogenolysis or hydroformylation or acid catalyzed dehydration.
Examples of chemicals produced from biomass include: substitute natural gas, biofuels, such as ethanol and bio-diesel, food browning materials, and commercial chemicals, such as diols (ethylene glycol and propylene glycol), acids (lactic acid, acrylic acid, and levulinic acid) and a wide range of other important chemical intermediates (epichlorohydrin, isoprene, furfural, and synthesis gas).
Within the field of pyrolysis, efforts have been focused on using feedstocks based on solid biomass and other cellulosic materials for producing the above chemicals.
Some efforts have been made to use sugars as feedstock for producing food browning materials, which comprise a large amount of glycolaldehyde (also termed hydroxyacetealdehyde) as the key browning agent.
U.S. Pat. No. 5,397,582 and the corresponding WO 92/17076 (Underwood) describes a method for preparation of ‘liquid smoke’ for browning foodstuffs by injecting sugar and/or starch into two alternative types of gas-solid contact reactors. One reactor hype is a ‘downer’ type, where the sugar is contacted with the heat carrier (e.g. sand) to produce pyrolysis products, and another is an up-flow type fluidized bed reactor. In the latter reactor the feedstock is injected into heat carrier particles in the form of sand. During the thermolytic fragmentation, a product vapour is formed. The stream of product vapour and spent heat carrier particles is transferred to two consecutive external cyclones and the resulting vapour stream is condensed. The heat carrier particles including char residues are recycled from the first stage cyclone to the bottom of the fragmentation reactor. The residence time of the product vapours is from 0.03 to 2 seconds, the fragmentation temperature is 400-1000° C., and quenching of pyrolysis vapours to less than 300° C. takes place within less than 0.6 s. It is unclear how the heat for reheating spent heat carrier particles is provided. Pyrolyzing powdered starch in this apparatus at 550° C. provides a pyrolysis liquid wherein half of the organics recovered was glycolaldehyde.
U.S. Pat. No. 7,094,932 (Majerski) describes a method of producing a food browning ingredient by thermolytic fragmentation of an aqueous solution of sugar, and in particular glucose, into a pyrolysis product with a high concentration of glycolaldehyde. The method uses a dense fluidized bed of sand particles (also referred to as a bubbling bed). The glucose solution comprising 25-99% of water is introduced into the reactor bed and reacted at a temperature of 500-600° C. The residence time in the reactor is suggested to be 0.1-5 seconds. The heat is provided by electrical heating. The gaseous reaction product is condensed in a surface condenser. The yields of glycolaldehyde in the condensed liquid fragmentation product are on mass basis at least 50% by weight of sugar fed to the reactor. The liquid fragmentation product comprises C1-C3 oxygenate compounds including formaldehyde, glycolaldehyde, glyoxal, pyruvaldehyde and acetol. The main product of this reaction is glycolaldehyde, and carbon recovery in condensate of up to 85-89% of the sugar feed has been achieved. In example 6 of U.S. Pat. No. 7,094,932 the method was scaled up by feeding 7.3 kg/hr of a feed containing 50% dextrose monohydrate (glucose) to a larger apparatus of the same type as above, providing a glycolaldehyde yield of 66%. The residence time in this system was 2-3 seconds and the temperature was in the range of 530-560° C. The heat was still provided by electricity.
WO 2014/131764 describes a method of producing ketene from a sugar solution by subjecting the sugar solution to pyrolysis in the presence of a fluidized bed material with a surface area of up to 600 m2/g and at a temperature of less than 700° C. The fluidized bed material is silica and the residence time is 50-150 ms
Both Underwood and Majerski have proposed systems for producing a glycolaldehyde rich product by pyrolysing sugars in a reactor using sand particles as heat carriers and having a short residence time in order to provide high conversion rates of the sugar into glycolaldehyde. However, the systems suggested are not suitable for industrial scale conversion of sugars into glycolaldehyde rich C1-C3 oxygenate mixtures by thermolytic fragmentation.
Fluidized bed reactors are used for processing a variety of feedstocks. They can be operated in a number of different fluidization regimens. The preferred regime is selected depending on the feedstock in question and the desired chemistry to be obtained, which gives rise to a large number of different reactor configurations for fluidized bed reactors.
For conversion of biomass into bio-oil by pyrolysis several reactor configurations have been investigated, such as e.g. dense phase (i.e. bubbling fluidized bed) and dilute phase (i.e. riser) reactors as well as radically different reactor types, such as ablative pyrolysis reactors.
WO 2012/115754 describes a pyrolysis method where solid biomass, such as wood or other plant derived material and a solid heat carrier, such as sand, are mixed at the bottom of a riser reactor and subjected to pyrolysis conditions, to provide a pyrolysis effluent. The pyrolysis effluent is led to a cyclone separator where it is separated into (1) a solids-enriched fraction comprising both solid char and a recycled portion of the solid heat carrier and (2) a solids-depleted fraction comprising pyrolysis products. The pyrolysis products include raw pyrolysis oil and other valuable chemicals, such as carboxylic acids, phenolics, and ketones. The solids-enriched fraction is directed to a reheater reactor comprising a fluidized bed of heat carrier particles wherein the solid char by-product is combusted in the presence of an oxygen containing gas and a quench medium is added in order to reduce the temperature in the reheater reactor. Reheated solid heat carrier is recycled to the pyrolysis riser reactor, where heat carrier particles in turn transfer heat to the pyrolysis reaction mixture to drive the pyrolysis reaction. The vaporous pyrolysis products are cooled and recovered.
Other applications of fluidized beds are for the cracking of hydrocarbons either catalytically of thermally. Catalytic cracking can be performed by the Fluid Catalytic Cracking (FCC) process, where high-boiling petroleum fractions are converted into comparatively lighter products, such as gasoline. Examples of thermal cracking are the Fluid Coking process, where heavy oil fractions, i.e. pitch, is converted into gas oil, or Thermal Cracking processes, where naphtha is converted into ethylene and propylene. These cracking processes are mostly performed in circulating fluidized bed systems
One such apparatus suitable for cracking light and heavy FCC feedstocks is described in U.S. Pat. No. 5,302,280 (Lomas). The system described includes a riser reactor for cracking the feedstock using a catalyst. After cracking, the catalyst particles are separated from the vapours and transported to a regenerator reactor, and the vapours are quenched. The catalyst particles are contacted with an oxygen containing stream in a dense fluidized bed resulting in combustion of residual coke to provide heat to the catalyst and to remove the coke from the catalyst particles.
Accordingly, new uses of C1-C3 oxygenate products are being developed and an increasing demand for those products are expected. Such oxygenate products may e.g. be used for producing ethylene glycol and propylene glycol by subjecting the oxygenate product to hydrogenation (see e.g. WO 2016/001169) or for scavenging hydrogen sulphide as described in WO 2017/064267. However, many other uses may be envisaged. To the best of our knowledge, no systems nor processes exist which are in fact suitable for large scale thermolytic conversion of sugars into glycolaldehyde rich mixtures in high yields.
Thus there is still a need for a high yielding and improved process for the preparation of C1-C3 oxygenates from sugars suitable for large scale production, as well as for systems for use in such processes.